ABSTRACT. Semantics of predicate formulas based on the notion of modified realizability for arithmetic formulas and interpretations of the language of arithmetic in all finite types are considered. For a number of natural constructive interpretations, the corresponding predicate logic of modified realizability is proved to be nonarithmetical.KEY WORDS: modified realizability, arithmetic in all finite types, constructive logic.w IntroductionThe notion of recursive reaiizability for arithmetic formulas introduced by Kleene in [1] proved to be a useful tool in the study of intuitionistic theories. This notion can also be regarded as a special kind of semantics of arithmetic sentences. It is this semantics that underlies the constructive trend in mathematics developed by A. A. Markov and his school [2].In connection with the development of constructive mathematics, it is of interest to describe the logical laws admissible from the constructive point of view. The greatest progress in the description of the laws of constructive propositional logic was achieved by Varpakhovskii [3], who created a calculus in which all realizable propositional formulas known to date are deducible. Whether this calculus is complete remains an open question. The predicate logic of recursive realizability turned out to be rather complicated: it is not enumerable and even not arithmetical (see [4,5]).Recently, interest in constructive semantics has grown in connection with program synthesis. It is known that an intuitionistic proof of an arithmetic sentence of the form Vx 3yP(x, y) can be reworked into an algorithm that for any rn constructs an n such that P(m, n) holds. Constructive semantics of the arithmetic language are commonly used to derive algorithms from intuitionistic proofs. A number of constructive semantics can be obtained by means of a suitable generalization of recursive realizability. One of these generalizations is the modified realizability introduced by Kreisel [6]. It is a translation from the language of first order arithmetic into that of arithmetic in all finite types, which associates to each formula F a specially defined formula mr F in the language of arithmetic in all finite types. Having chosen some interpretation of the language of arithmetic in all finite types, we can define a semantics of arithmetic formulas by assuming a closed arithmetic formula F to be true (or M-realizable) if the formula mr F is true in the interpretation M.We can consider the predicate logic corresponding to the semantics thus obtained, that is, the collection of the predicate formulas all of whose arithmetic instances are true (M-realizable) for this semantics. These predicate formulas will also be called M-realizable. The aim of this paper is to show that for a number of natural interpretations of M the set of all M-realizable predicate formulas is not arithmetical. The proof of this fact is based on a formalization of the Tennenbaum theorem [7] according to which recursive nonstandard models of arithmetic are impossible.In w we des...